<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body{
            /* white-space: pre; */
        }
    </style>
</head>
<body>
    
</body>
<script>
    // test()    
    // exec() 


    // 元字符
    // 限定符   {n}   {n,}  {n,m}  *   +   ?
    // 定位符   ^     $
    // 字符匹配符   [xyz]  [0-9]   [0-9a-zA-Z_]    [^xyz]  [^0-9]   [^0-9a-zA-Z_]
    //                     \d      \w                       \D        \W          \s    [\u4e00-\u9fa5]

    // 选择匹配符  |

    // \s   [\n\r\f\t\v]
    // \S   [^\n\r\f\t\v]
    // .    [^\n]


    // console.log("hello world, \n Today \r is \f Friday!");
    // document.write("hello world, \n Today \r is  Friday!");
    document.body.innerHTML = "hello world, \n Today \r is \f  \t   Friday!";





</script>
</html>